The present invention relates to investment casting of metals and alloys in ceramic shell molds fabricated using a fugitive pattern of the article to be cast.
In investment casting superalloy gas turbine engine blades and vanes using conventional equiaxed and directional solidification techniques, ceramic investment shell molds with or without a ceramic core therein are filled with molten metal or alloy that is solidified in the mold. The ceramic shell mold is made by the well known lost-wax process where a fugitive (e.g. wax, thermoplastic, etc.) pattern of the blade, vane or other article to be cast is repeatedly dipped in a ceramic slurry, drained of excess slurry and then stuccoed with ceramic particulates, such as ceramic sand (stucco) to build up the shell mold wall thickness to a desired value. The pattern then is selectively removed from the shell mold by thermal or chemical dewaxing techniques, and the green mold is fired to develop adequate mold strength for casting. U.S. Pat. Nos. 5,335,717 and 5,975,188 describe a typical lost-process sequence to make ceramic investment casting shell molds.
After molten metal or alloy is cast in the shell mold and solidified, the investment casting is removed and subjected to one or more post-casting operations including, but not limited to, removing of any ceramic core present, grit blasting to remove remnant ceramic shell mold material, heat treatment to develop casting mechanical properties, hot isostatic pressing to close casting porosity, acid etching to inspect the metal or alloy microstructure, and anodic etching to inspect the surface for defects.
Current practice in investment casting superalloy gas turbine engine blades and vanes using conventional equiaxed and directional solidification techniques is to provide a process routing sheet that includes a part identification number (e.g. serial number) and that is carried through the manufacturing process from the pattern stage through the post-casting operation stage.
An object of the present invention is to provide for investment casting of a plurality of metallic articles where a relief pattern comprising a three dimensional bar code representing a unique part identification number is provided on each fugitive pattern and is transferred first to each shell mold and then to each metallic article cast in that shell mold such that the bar code is cast-in-place permanently on each investment cast article in a manner that the bar code on the investment cast articles will survive post-casting production operations to provide a readable, unique bar code on each shipped investment cast article.
In an embodiment of the invention, a plastic identification tag bearing the unique bar code is attached to a surface of each fugitive pattern. For example, a polymeric identification tag bearing the unique bar code is wax welded to a surface of each wax pattern of the article to be cast followed by processing pursuant to the lost wax process to build up a ceramic shell mold on the pattern. The plastic identification tag is removed from the shell mold or destroyed with the fugitive pattern is removed from the shell mold. In another embodiment of the invention, a unique three dimensional bar code is engraved, embossed or otherwise formed in a surface of each fugitive pattern. The unique bar code is transferred to the shell mold and then to the cast metallic article and remains permanently thereon through post-casting production operations and on the shipped cast article representative of a unique part identification number thereon.
The invention is advantageous to provide on each investment cast metallic article a permanent unique three dimensional bar code that is readable as a part identification number to permit part tracking and traceability during and after manufacture of each article. The presence of the bar code on the fugitive pattern, shell mold, and investment cast article eliminates the need for machine operators to input into the process routing a part identification number at each work station. Moreover, the presence of the unique bar code on each investment cast article shipped to customers will permit the customer(s) to access the manufacturer""s part tracing computer system in which the part identification code is stored in conjunction with associated part dimensional and processing data.
The above objects and advantages of the present invention will become more readily apparent from the following detailed description taken with the following drawings.